'\" t
.\"     Title: CREATE TABLE
.\"    Author: The PostgreSQL Global Development Group
.\" Generator: DocBook XSL Stylesheets v1.75.2 <http://docbook.sf.net/>
.\"      Date: 2011-12-01
.\"    Manual: PostgreSQL 9.1.2 Documentation
.\"    Source: PostgreSQL 9.1.2
.\"  Language: English
.\"
.TH "CREATE TABLE" "7" "2011-12-01" "PostgreSQL 9.1.2" "PostgreSQL 9.1.2 Documentation"
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.SH "NAME"
CREATE_TABLE \- define a new table
.\" CREATE TABLE
.SH "SYNOPSIS"
.sp
.nf
CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXISTS ] \fItable_name\fR ( [
  { \fIcolumn_name\fR \fIdata_type\fR [ COLLATE \fIcollation\fR ] [ \fIcolumn_constraint\fR [ \&.\&.\&. ] ]
    | \fItable_constraint\fR
    | LIKE \fIparent_table\fR [ \fIlike_option\fR \&.\&.\&. ] }
    [, \&.\&.\&. ]
] )
[ INHERITS ( \fIparent_table\fR [, \&.\&.\&. ] ) ]
[ WITH ( \fIstorage_parameter\fR [= \fIvalue\fR] [, \&.\&.\&. ] ) | WITH OIDS | WITHOUT OIDS ]
[ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ]
[ TABLESPACE \fItablespace\fR ]

CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXISTS ] \fItable_name\fR
    OF \fItype_name\fR [ (
  { \fIcolumn_name\fR WITH OPTIONS [ \fIcolumn_constraint\fR [ \&.\&.\&. ] ]
    | \fItable_constraint\fR }
    [, \&.\&.\&. ]
) ]
[ WITH ( \fIstorage_parameter\fR [= \fIvalue\fR] [, \&.\&.\&. ] ) | WITH OIDS | WITHOUT OIDS ]
[ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ]
[ TABLESPACE \fItablespace\fR ]

where \fIcolumn_constraint\fR is:

[ CONSTRAINT \fIconstraint_name\fR ]
{ NOT NULL |
  NULL |
  CHECK ( \fIexpression\fR ) |
  DEFAULT \fIdefault_expr\fR |
  UNIQUE \fIindex_parameters\fR |
  PRIMARY KEY \fIindex_parameters\fR |
  REFERENCES \fIreftable\fR [ ( \fIrefcolumn\fR ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ]
    [ ON DELETE \fIaction\fR ] [ ON UPDATE \fIaction\fR ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]

and \fItable_constraint\fR is:

[ CONSTRAINT \fIconstraint_name\fR ]
{ CHECK ( \fIexpression\fR ) |
  UNIQUE ( \fIcolumn_name\fR [, \&.\&.\&. ] ) \fIindex_parameters\fR |
  PRIMARY KEY ( \fIcolumn_name\fR [, \&.\&.\&. ] ) \fIindex_parameters\fR |
  EXCLUDE [ USING \fIindex_method\fR ] ( \fIexclude_element\fR WITH \fIoperator\fR [, \&.\&.\&. ] ) \fIindex_parameters\fR [ WHERE ( \fIpredicate\fR ) ] |
  FOREIGN KEY ( \fIcolumn_name\fR [, \&.\&.\&. ] ) REFERENCES \fIreftable\fR [ ( \fIrefcolumn\fR [, \&.\&.\&. ] ) ]
    [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ ON DELETE \fIaction\fR ] [ ON UPDATE \fIaction\fR ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]

and \fIlike_option\fR is:

{ INCLUDING | EXCLUDING } { DEFAULTS | CONSTRAINTS | INDEXES | STORAGE | COMMENTS | ALL }

\fIindex_parameters\fR in UNIQUE, PRIMARY KEY, and EXCLUDE constraints are:

[ WITH ( \fIstorage_parameter\fR [= \fIvalue\fR] [, \&.\&.\&. ] ) ]
[ USING INDEX TABLESPACE \fItablespace\fR ]

\fIexclude_element\fR in an EXCLUDE constraint is:

{ \fIcolumn\fR | ( \fIexpression\fR ) } [ \fIopclass\fR ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ]
.fi
.SH "DESCRIPTION"
.PP

CREATE TABLE
will create a new, initially empty table in the current database\&. The table will be owned by the user issuing the command\&.
.PP
If a schema name is given (for example,
CREATE TABLE myschema\&.mytable \&.\&.\&.) then the table is created in the specified schema\&. Otherwise it is created in the current schema\&. Temporary tables exist in a special schema, so a schema name cannot be given when creating a temporary table\&. The name of the table must be distinct from the name of any other table, sequence, index, view, or foreign table in the same schema\&.
.PP

CREATE TABLE
also automatically creates a data type that represents the composite type corresponding to one row of the table\&. Therefore, tables cannot have the same name as any existing data type in the same schema\&.
.PP
The optional constraint clauses specify constraints (tests) that new or updated rows must satisfy for an insert or update operation to succeed\&. A constraint is an SQL object that helps define the set of valid values in the table in various ways\&.
.PP
There are two ways to define constraints: table constraints and column constraints\&. A column constraint is defined as part of a column definition\&. A table constraint definition is not tied to a particular column, and it can encompass more than one column\&. Every column constraint can also be written as a table constraint; a column constraint is only a notational convenience for use when the constraint only affects one column\&.
.SH "PARAMETERS"
.PP
TEMPORARY or TEMP
.RS 4
If specified, the table is created as a temporary table\&. Temporary tables are automatically dropped at the end of a session, or optionally at the end of the current transaction (see
ON COMMIT
below)\&. Existing permanent tables with the same name are not visible to the current session while the temporary table exists, unless they are referenced with schema\-qualified names\&. Any indexes created on a temporary table are automatically temporary as well\&.
.sp
The
autovacuum daemon
cannot access and therefore cannot vacuum or analyze temporary tables\&. For this reason, appropriate vacuum and analyze operations should be performed via session SQL commands\&. For example, if a temporary table is going to be used in complex queries, it is wise to run
ANALYZE
on the temporary table after it is populated\&.
.sp
Optionally,
GLOBAL
or
LOCAL
can be written before
TEMPORARY
or
TEMP\&. This makes no difference in
PostgreSQL, but see
COMPATIBILITY\&.
.RE
.PP
UNLOGGED
.RS 4
If specified, the table is created as an unlogged table\&. Data written to unlogged tables is not written to the write\-ahead log (see
Chapter 29, Reliability and the Write-Ahead Log, in the documentation), which makes them considerably faster than ordinary tables\&. However, they are not crash\-safe: an unlogged table is automatically truncated after a crash or unclean shutdown\&. The contents of an unlogged table are also not replicated to standby servers\&. Any indexes created on an unlogged table are automatically unlogged as well; however, unlogged
GiST indexes
are currently not supported and cannot be created on an unlogged table\&.
.RE
.PP
IF NOT EXISTS
.RS 4
Do not throw an error if a relation with the same name already exists\&. A notice is issued in this case\&. Note that there is no guarantee that the existing relation is anything like the one that would have been created\&.
.RE
.PP
\fItable_name\fR
.RS 4
The name (optionally schema\-qualified) of the table to be created\&.
.RE
.PP
OF \fItype_name\fR
.RS 4
Creates a
typed table, which takes its structure from the specified composite type (name optionally schema\-qualified)\&. A typed table is tied to its type; for example the table will be dropped if the type is dropped (with
DROP TYPE \&.\&.\&. CASCADE)\&.
.sp
When a typed table is created, then the data types of the columns are determined by the underlying composite type and are not specified by the
CREATE TABLE
command\&. But the
CREATE TABLE
command can add defaults and constraints to the table and can specify storage parameters\&.
.RE
.PP
\fIcolumn_name\fR
.RS 4
The name of a column to be created in the new table\&.
.RE
.PP
\fIdata_type\fR
.RS 4
The data type of the column\&. This can include array specifiers\&. For more information on the data types supported by
PostgreSQL, refer to
Chapter 8, Data Types, in the documentation\&.
.RE
.PP
COLLATE \fIcollation\fR
.RS 4
The
COLLATE
clause assigns a collation to the column (which must be of a collatable data type)\&. If not specified, the column data type\*(Aqs default collation is used\&.
.RE
.PP
INHERITS ( \fIparent_table\fR [, \&.\&.\&. ] )
.RS 4
The optional
INHERITS
clause specifies a list of tables from which the new table automatically inherits all columns\&.
.sp
Use of
INHERITS
creates a persistent relationship between the new child table and its parent table(s)\&. Schema modifications to the parent(s) normally propagate to children as well, and by default the data of the child table is included in scans of the parent(s)\&.
.sp
If the same column name exists in more than one parent table, an error is reported unless the data types of the columns match in each of the parent tables\&. If there is no conflict, then the duplicate columns are merged to form a single column in the new table\&. If the column name list of the new table contains a column name that is also inherited, the data type must likewise match the inherited column(s), and the column definitions are merged into one\&. If the new table explicitly specifies a default value for the column, this default overrides any defaults from inherited declarations of the column\&. Otherwise, any parents that specify default values for the column must all specify the same default, or an error will be reported\&.
.sp
CHECK
constraints are merged in essentially the same way as columns: if multiple parent tables and/or the new table definition contain identically\-named
CHECK
constraints, these constraints must all have the same check expression, or an error will be reported\&. Constraints having the same name and expression will be merged into one copy\&. Notice that an unnamed
CHECK
constraint in the new table will never be merged, since a unique name will always be chosen for it\&.
.sp
Column
STORAGE
settings are also copied from parent tables\&.
.RE
.PP
LIKE \fIparent_table\fR [ \fIlike_option\fR \&.\&.\&. ]
.RS 4
The
LIKE
clause specifies a table from which the new table automatically copies all column names, their data types, and their not\-null constraints\&.
.sp
Unlike
INHERITS, the new table and original table are completely decoupled after creation is complete\&. Changes to the original table will not be applied to the new table, and it is not possible to include data of the new table in scans of the original table\&.
.sp
Default expressions for the copied column definitions will only be copied if
INCLUDING DEFAULTS
is specified\&. The default behavior is to exclude default expressions, resulting in the copied columns in the new table having null defaults\&.
.sp
Not\-null constraints are always copied to the new table\&.
CHECK
constraints will only be copied if
INCLUDING CONSTRAINTS
is specified; other types of constraints will never be copied\&. Also, no distinction is made between column constraints and table constraints \(em when constraints are requested, all check constraints are copied\&.
.sp
Any indexes on the original table will not be created on the new table, unless the
INCLUDING INDEXES
clause is specified\&.
.sp
STORAGE
settings for the copied column definitions will only be copied if
INCLUDING STORAGE
is specified\&. The default behavior is to exclude
STORAGE
settings, resulting in the copied columns in the new table having type\-specific default settings\&. For more on
STORAGE
settings, see
Section 55.2, \(lqTOAST\(rq, in the documentation\&.
.sp
Comments for the copied columns, constraints, and indexes will only be copied if
INCLUDING COMMENTS
is specified\&. The default behavior is to exclude comments, resulting in the copied columns and constraints in the new table having no comments\&.
.sp
INCLUDING ALL
is an abbreviated form of
INCLUDING DEFAULTS INCLUDING CONSTRAINTS INCLUDING INDEXES INCLUDING STORAGE INCLUDING COMMENTS\&.
.sp
Note also that unlike
INHERITS, columns and constraints copied by
LIKE
are not merged with similarly named columns and constraints\&. If the same name is specified explicitly or in another
LIKE
clause, an error is signalled\&.
.RE
.PP
CONSTRAINT \fIconstraint_name\fR
.RS 4
An optional name for a column or table constraint\&. If the constraint is violated, the constraint name is present in error messages, so constraint names like
col must be positive
can be used to communicate helpful constraint information to client applications\&. (Double\-quotes are needed to specify constraint names that contain spaces\&.) If a constraint name is not specified, the system generates a name\&.
.RE
.PP
NOT NULL
.RS 4
The column is not allowed to contain null values\&.
.RE
.PP
NULL
.RS 4
The column is allowed to contain null values\&. This is the default\&.
.sp
This clause is only provided for compatibility with non\-standard SQL databases\&. Its use is discouraged in new applications\&.
.RE
.PP
CHECK ( \fIexpression\fR )
.RS 4
The
CHECK
clause specifies an expression producing a Boolean result which new or updated rows must satisfy for an insert or update operation to succeed\&. Expressions evaluating to TRUE or UNKNOWN succeed\&. Should any row of an insert or update operation produce a FALSE result an error exception is raised and the insert or update does not alter the database\&. A check constraint specified as a column constraint should reference that column\*(Aqs value only, while an expression appearing in a table constraint can reference multiple columns\&.
.sp
Currently,
CHECK
expressions cannot contain subqueries nor refer to variables other than columns of the current row\&.
.RE
.PP
DEFAULT \fIdefault_expr\fR
.RS 4
The
DEFAULT
clause assigns a default data value for the column whose column definition it appears within\&. The value is any variable\-free expression (subqueries and cross\-references to other columns in the current table are not allowed)\&. The data type of the default expression must match the data type of the column\&.
.sp
The default expression will be used in any insert operation that does not specify a value for the column\&. If there is no default for a column, then the default is null\&.
.RE
.PP
UNIQUE (column constraint), UNIQUE ( \fIcolumn_name\fR [, \&.\&.\&. ] ) (table constraint)
.RS 4
The
UNIQUE
constraint specifies that a group of one or more columns of a table can contain only unique values\&. The behavior of the unique table constraint is the same as that for column constraints, with the additional capability to span multiple columns\&.
.sp
For the purpose of a unique constraint, null values are not considered equal\&.
.sp
Each unique table constraint must name a set of columns that is different from the set of columns named by any other unique or primary key constraint defined for the table\&. (Otherwise it would just be the same constraint listed twice\&.)
.RE
.PP
PRIMARY KEY (column constraint), PRIMARY KEY ( \fIcolumn_name\fR [, \&.\&.\&. ] ) (table constraint)
.RS 4
The primary key constraint specifies that a column or columns of a table can contain only unique (non\-duplicate), nonnull values\&. Technically,
PRIMARY KEY
is merely a combination of
UNIQUE
and
NOT NULL, but identifying a set of columns as primary key also provides metadata about the design of the schema, as a primary key implies that other tables can rely on this set of columns as a unique identifier for rows\&.
.sp
Only one primary key can be specified for a table, whether as a column constraint or a table constraint\&.
.sp
The primary key constraint should name a set of columns that is different from other sets of columns named by any unique constraint defined for the same table\&.
.RE
.PP
EXCLUDE [ USING \fIindex_method\fR ] ( \fIexclude_element\fR WITH \fIoperator\fR [, \&.\&.\&. ] ) \fIindex_parameters\fR [ WHERE ( \fIpredicate\fR ) ]
.RS 4
The
EXCLUDE
clause defines an exclusion constraint, which guarantees that if any two rows are compared on the specified column(s) or expression(s) using the specified operator(s), not all of these comparisons will return
TRUE\&. If all of the specified operators test for equality, this is equivalent to a
UNIQUE
constraint, although an ordinary unique constraint will be faster\&. However, exclusion constraints can specify constraints that are more general than simple equality\&. For example, you can specify a constraint that no two rows in the table contain overlapping circles (see
Section 8.8, \(lqGeometric Types\(rq, in the documentation) by using the
&&
operator\&.
.sp
Exclusion constraints are implemented using an index, so each specified operator must be associated with an appropriate operator class (see
Section 11.9, \(lqOperator Classes and Operator Families\(rq, in the documentation) for the index access method
\fIindex_method\fR\&. The operators are required to be commutative\&. Each
\fIexclude_element\fR
can optionally specify an operator class and/or ordering options; these are described fully under
CREATE INDEX (\fBCREATE_INDEX\fR(7))\&.
.sp
The access method must support
amgettuple
(see
Chapter 52, Index Access Method Interface Definition, in the documentation); at present this means
GIN
cannot be used\&. Although it\*(Aqs allowed, there is little point in using B\-tree or hash indexes with an exclusion constraint, because this does nothing that an ordinary unique constraint doesn\*(Aqt do better\&. So in practice the access method will always be
GiST\&.
.sp
The
\fIpredicate\fR
allows you to specify an exclusion constraint on a subset of the table; internally this creates a partial index\&. Note that parentheses are required around the predicate\&.
.RE
.PP
REFERENCES \fIreftable\fR [ ( \fIrefcolumn\fR ) ] [ MATCH \fImatchtype\fR ] [ ON DELETE \fIaction\fR ] [ ON UPDATE \fIaction\fR ] (column constraint), FOREIGN KEY ( \fIcolumn\fR [, \&.\&.\&. ] ) REFERENCES \fIreftable\fR [ ( \fIrefcolumn\fR [, \&.\&.\&. ] ) ] [ MATCH \fImatchtype\fR ] [ ON DELETE \fIaction\fR ] [ ON UPDATE \fIaction\fR ] (table constraint)
.RS 4
These clauses specify a foreign key constraint, which requires that a group of one or more columns of the new table must only contain values that match values in the referenced column(s) of some row of the referenced table\&. If
\fIrefcolumn\fR
is omitted, the primary key of the
\fIreftable\fR
is used\&. The referenced columns must be the columns of a non\-deferrable unique or primary key constraint in the referenced table\&. Note that foreign key constraints cannot be defined between temporary tables and permanent tables\&.
.sp
A value inserted into the referencing column(s) is matched against the values of the referenced table and referenced columns using the given match type\&. There are three match types:
MATCH FULL,
MATCH PARTIAL, and
MATCH SIMPLE, which is also the default\&.
MATCH FULL
will not allow one column of a multicolumn foreign key to be null unless all foreign key columns are null\&.
MATCH SIMPLE
allows some foreign key columns to be null while other parts of the foreign key are not null\&.
MATCH PARTIAL
is not yet implemented\&.
.sp
In addition, when the data in the referenced columns is changed, certain actions are performed on the data in this table\*(Aqs columns\&. The
ON DELETE
clause specifies the action to perform when a referenced row in the referenced table is being deleted\&. Likewise, the
ON UPDATE
clause specifies the action to perform when a referenced column in the referenced table is being updated to a new value\&. If the row is updated, but the referenced column is not actually changed, no action is done\&. Referential actions other than the
NO ACTION
check cannot be deferred, even if the constraint is declared deferrable\&. There are the following possible actions for each clause:
.PP
NO ACTION
.RS 4
Produce an error indicating that the deletion or update would create a foreign key constraint violation\&. If the constraint is deferred, this error will be produced at constraint check time if there still exist any referencing rows\&. This is the default action\&.
.RE
.PP
RESTRICT
.RS 4
Produce an error indicating that the deletion or update would create a foreign key constraint violation\&. This is the same as
NO ACTION
except that the check is not deferrable\&.
.RE
.PP
CASCADE
.RS 4
Delete any rows referencing the deleted row, or update the value of the referencing column to the new value of the referenced column, respectively\&.
.RE
.PP
SET NULL
.RS 4
Set the referencing column(s) to null\&.
.RE
.PP
SET DEFAULT
.RS 4
Set the referencing column(s) to their default values\&.
.RE
.sp
If the referenced column(s) are changed frequently, it might be wise to add an index to the foreign key column so that referential actions associated with the foreign key column can be performed more efficiently\&.
.RE
.PP
DEFERRABLE, NOT DEFERRABLE
.RS 4
This controls whether the constraint can be deferred\&. A constraint that is not deferrable will be checked immediately after every command\&. Checking of constraints that are deferrable can be postponed until the end of the transaction (using the
SET CONSTRAINTS (\fBSET_CONSTRAINTS\fR(7))
command)\&.
NOT DEFERRABLE
is the default\&. Currently, only
UNIQUE,
PRIMARY KEY,
EXCLUDE, and
REFERENCES
(foreign key) constraints accept this clause\&.
NOT NULL
and
CHECK
constraints are not deferrable\&.
.RE
.PP
INITIALLY IMMEDIATE, INITIALLY DEFERRED
.RS 4
If a constraint is deferrable, this clause specifies the default time to check the constraint\&. If the constraint is
INITIALLY IMMEDIATE, it is checked after each statement\&. This is the default\&. If the constraint is
INITIALLY DEFERRED, it is checked only at the end of the transaction\&. The constraint check time can be altered with the
SET CONSTRAINTS (\fBSET_CONSTRAINTS\fR(7))
command\&.
.RE
.PP
WITH ( \fIstorage_parameter\fR [= \fIvalue\fR] [, \&.\&.\&. ] )
.RS 4
This clause specifies optional storage parameters for a table or index; see
Storage Parameters
for more information\&. The
WITH
clause for a table can also include
OIDS=TRUE
(or just
OIDS) to specify that rows of the new table should have OIDs (object identifiers) assigned to them, or
OIDS=FALSE
to specify that the rows should not have OIDs\&. If
OIDS
is not specified, the default setting depends upon the
default_with_oids
configuration parameter\&. (If the new table inherits from any tables that have OIDs, then
OIDS=TRUE
is forced even if the command says
OIDS=FALSE\&.)
.sp
If
OIDS=FALSE
is specified or implied, the new table does not store OIDs and no OID will be assigned for a row inserted into it\&. This is generally considered worthwhile, since it will reduce OID consumption and thereby postpone the wraparound of the 32\-bit OID counter\&. Once the counter wraps around, OIDs can no longer be assumed to be unique, which makes them considerably less useful\&. In addition, excluding OIDs from a table reduces the space required to store the table on disk by 4 bytes per row (on most machines), slightly improving performance\&.
.sp
To remove OIDs from a table after it has been created, use
ALTER TABLE (\fBALTER_TABLE\fR(7))\&.
.RE
.PP
WITH OIDS, WITHOUT OIDS
.RS 4
These are obsolescent syntaxes equivalent to
WITH (OIDS)
and
WITH (OIDS=FALSE), respectively\&. If you wish to give both an
OIDS
setting and storage parameters, you must use the
WITH ( \&.\&.\&. )
syntax; see above\&.
.RE
.PP
ON COMMIT
.RS 4
The behavior of temporary tables at the end of a transaction block can be controlled using
ON COMMIT\&. The three options are:
.PP
PRESERVE ROWS
.RS 4
No special action is taken at the ends of transactions\&. This is the default behavior\&.
.RE
.PP
DELETE ROWS
.RS 4
All rows in the temporary table will be deleted at the end of each transaction block\&. Essentially, an automatic
\fBTRUNCATE\fR(7)
is done at each commit\&.
.RE
.PP
DROP
.RS 4
The temporary table will be dropped at the end of the current transaction block\&.
.RE
.RE
.PP
TABLESPACE \fItablespace\fR
.RS 4
The
\fItablespace\fR
is the name of the tablespace in which the new table is to be created\&. If not specified,
default_tablespace
is consulted, or
temp_tablespaces
if the table is temporary\&.
.RE
.PP
USING INDEX TABLESPACE \fItablespace\fR
.RS 4
This clause allows selection of the tablespace in which the index associated with a
UNIQUE,
PRIMARY KEY, or
EXCLUDE
constraint will be created\&. If not specified,
default_tablespace
is consulted, or
temp_tablespaces
if the table is temporary\&.
.RE
.SS "Storage Parameters"
.\" storage parameters
.PP
The
WITH
clause can specify
storage parameters
for tables, and for indexes associated with a
UNIQUE,
PRIMARY KEY, or
EXCLUDE
constraint\&. Storage parameters for indexes are documented in
CREATE INDEX (\fBCREATE_INDEX\fR(7))\&. The storage parameters currently available for tables are listed below\&. For each parameter, unless noted, there is an additional parameter with the same name prefixed with
toast\&., which can be used to control the behavior of the table\*(Aqs secondary
TOAST
table, if any (see
Section 55.2, \(lqTOAST\(rq, in the documentation
for more information about TOAST)\&. Note that the TOAST table inherits the
autovacuum_*
values from its parent table, if there are no
toast\&.autovacuum_*
settings set\&.
.PP
fillfactor (integer)
.RS 4
The fillfactor for a table is a percentage between 10 and 100\&. 100 (complete packing) is the default\&. When a smaller fillfactor is specified,
INSERT
operations pack table pages only to the indicated percentage; the remaining space on each page is reserved for updating rows on that page\&. This gives
UPDATE
a chance to place the updated copy of a row on the same page as the original, which is more efficient than placing it on a different page\&. For a table whose entries are never updated, complete packing is the best choice, but in heavily updated tables smaller fillfactors are appropriate\&. This parameter cannot be set for TOAST tables\&.
.RE
.PP
autovacuum_enabled, toast\&.autovacuum_enabled (boolean)
.RS 4
Enables or disables the autovacuum daemon on a particular table\&. If true, the autovacuum daemon will initiate a
VACUUM
operation on a particular table when the number of updated or deleted tuples exceeds
autovacuum_vacuum_threshold
plus
autovacuum_vacuum_scale_factor
times the number of live tuples currently estimated to be in the relation\&. Similarly, it will initiate an
ANALYZE
operation when the number of inserted, updated or deleted tuples exceeds
autovacuum_analyze_threshold
plus
autovacuum_analyze_scale_factor
times the number of live tuples currently estimated to be in the relation\&. If false, this table will not be autovacuumed, except to prevent transaction Id wraparound\&. See
Section 23.1.4, \(lqPreventing Transaction ID Wraparound Failures\(rq, in the documentation
for more about wraparound prevention\&. Observe that this variable inherits its value from the
autovacuum
setting\&.
.RE
.PP
autovacuum_vacuum_threshold, toast\&.autovacuum_vacuum_threshold (integer)
.RS 4
Minimum number of updated or deleted tuples before initiate a
VACUUM
operation on a particular table\&.
.RE
.PP
autovacuum_vacuum_scale_factor, toast\&.autovacuum_vacuum_scale_factor (float4)
.RS 4
Multiplier for
reltuples
to add to
autovacuum_vacuum_threshold\&.
.RE
.PP
autovacuum_analyze_threshold (integer)
.RS 4
Minimum number of inserted, updated, or deleted tuples before initiate an
ANALYZE
operation on a particular table\&.
.RE
.PP
autovacuum_analyze_scale_factor (float4)
.RS 4
Multiplier for
reltuples
to add to
autovacuum_analyze_threshold\&.
.RE
.PP
autovacuum_vacuum_cost_delay, toast\&.autovacuum_vacuum_cost_delay (integer)
.RS 4
Custom
autovacuum_vacuum_cost_delay
parameter\&.
.RE
.PP
autovacuum_vacuum_cost_limit, toast\&.autovacuum_vacuum_cost_limit (integer)
.RS 4
Custom
autovacuum_vacuum_cost_limit
parameter\&.
.RE
.PP
autovacuum_freeze_min_age, toast\&.autovacuum_freeze_min_age (integer)
.RS 4
Custom
vacuum_freeze_min_age
parameter\&. Note that autovacuum will ignore attempts to set a per\-table
autovacuum_freeze_min_age
larger than the half system\-wide
autovacuum_freeze_max_age
setting\&.
.RE
.PP
autovacuum_freeze_max_age, toast\&.autovacuum_freeze_max_age (integer)
.RS 4
Custom
autovacuum_freeze_max_age
parameter\&. Note that autovacuum will ignore attempts to set a per\-table
autovacuum_freeze_max_age
larger than the system\-wide setting (it can only be set smaller)\&. Note that while you can set
autovacuum_freeze_max_age
very small, or even zero, this is usually unwise since it will force frequent vacuuming\&.
.RE
.PP
autovacuum_freeze_table_age, toast\&.autovacuum_freeze_table_age (integer)
.RS 4
Custom
vacuum_freeze_table_age
parameter\&.
.RE
.SH "NOTES"
.PP
Using OIDs in new applications is not recommended: where possible, using a
SERIAL
or other sequence generator as the table\*(Aqs primary key is preferred\&. However, if your application does make use of OIDs to identify specific rows of a table, it is recommended to create a unique constraint on the
oid
column of that table, to ensure that OIDs in the table will indeed uniquely identify rows even after counter wraparound\&. Avoid assuming that OIDs are unique across tables; if you need a database\-wide unique identifier, use the combination of
tableoid
and row OID for the purpose\&.
.if n \{\
.sp
.\}
.RS 4
.it 1 an-trap
.nr an-no-space-flag 1
.nr an-break-flag 1
.br
.ps +1
\fBTip\fR
.ps -1
.br
.PP
The use of
OIDS=FALSE
is not recommended for tables with no primary key, since without either an OID or a unique data key, it is difficult to identify specific rows\&.
.sp .5v
.RE
.PP

PostgreSQL
automatically creates an index for each unique constraint and primary key constraint to enforce uniqueness\&. Thus, it is not necessary to create an index explicitly for primary key columns\&. (See
CREATE INDEX (\fBCREATE_INDEX\fR(7))
for more information\&.)
.PP
Unique constraints and primary keys are not inherited in the current implementation\&. This makes the combination of inheritance and unique constraints rather dysfunctional\&.
.PP
A table cannot have more than 1600 columns\&. (In practice, the effective limit is usually lower because of tuple\-length constraints\&.)
.SH "EXAMPLES"
.PP
Create table
films
and table
distributors:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE TABLE films (
    code        char(5) CONSTRAINT firstkey PRIMARY KEY,
    title       varchar(40) NOT NULL,
    did         integer NOT NULL,
    date_prod   date,
    kind        varchar(10),
    len         interval hour to minute
);

CREATE TABLE distributors (
     did    integer PRIMARY KEY DEFAULT nextval(\*(Aqserial\*(Aq),
     name   varchar(40) NOT NULL CHECK (name <> \*(Aq\*(Aq)
);
.fi
.if n \{\
.RE
.\}
.PP
Create a table with a 2\-dimensional array:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE TABLE array_int (
    vector  int[][]
);
.fi
.if n \{\
.RE
.\}
.PP
Define a unique table constraint for the table
films\&. Unique table constraints can be defined on one or more columns of the table:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE TABLE films (
    code        char(5),
    title       varchar(40),
    did         integer,
    date_prod   date,
    kind        varchar(10),
    len         interval hour to minute,
    CONSTRAINT production UNIQUE(date_prod)
);
.fi
.if n \{\
.RE
.\}
.PP
Define a check column constraint:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE TABLE distributors (
    did     integer CHECK (did > 100),
    name    varchar(40)
);
.fi
.if n \{\
.RE
.\}
.PP
Define a check table constraint:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE TABLE distributors (
    did     integer,
    name    varchar(40)
    CONSTRAINT con1 CHECK (did > 100 AND name <> \*(Aq\*(Aq)
);
.fi
.if n \{\
.RE
.\}
.PP
Define a primary key table constraint for the table
films:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE TABLE films (
    code        char(5),
    title       varchar(40),
    did         integer,
    date_prod   date,
    kind        varchar(10),
    len         interval hour to minute,
    CONSTRAINT code_title PRIMARY KEY(code,title)
);
.fi
.if n \{\
.RE
.\}
.PP
Define a primary key constraint for table
distributors\&. The following two examples are equivalent, the first using the table constraint syntax, the second the column constraint syntax:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE TABLE distributors (
    did     integer,
    name    varchar(40),
    PRIMARY KEY(did)
);

CREATE TABLE distributors (
    did     integer PRIMARY KEY,
    name    varchar(40)
);
.fi
.if n \{\
.RE
.\}
.PP
Assign a literal constant default value for the column
name, arrange for the default value of column
did
to be generated by selecting the next value of a sequence object, and make the default value of
modtime
be the time at which the row is inserted:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE TABLE distributors (
    name      varchar(40) DEFAULT \*(AqLuso Films\*(Aq,
    did       integer DEFAULT nextval(\*(Aqdistributors_serial\*(Aq),
    modtime   timestamp DEFAULT current_timestamp
);
.fi
.if n \{\
.RE
.\}
.PP
Define two
NOT NULL
column constraints on the table
distributors, one of which is explicitly given a name:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE TABLE distributors (
    did     integer CONSTRAINT no_null NOT NULL,
    name    varchar(40) NOT NULL
);
.fi
.if n \{\
.RE
.\}
.PP
Define a unique constraint for the
name
column:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE TABLE distributors (
    did     integer,
    name    varchar(40) UNIQUE
);
.fi
.if n \{\
.RE
.\}
.sp
The same, specified as a table constraint:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE TABLE distributors (
    did     integer,
    name    varchar(40),
    UNIQUE(name)
);
.fi
.if n \{\
.RE
.\}
.PP
Create the same table, specifying 70% fill factor for both the table and its unique index:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE TABLE distributors (
    did     integer,
    name    varchar(40),
    UNIQUE(name) WITH (fillfactor=70)
)
WITH (fillfactor=70);
.fi
.if n \{\
.RE
.\}
.PP
Create table
circles
with an exclusion constraint that prevents any two circles from overlapping:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE TABLE circles (
    c circle,
    EXCLUDE USING gist (c WITH &&)
);
.fi
.if n \{\
.RE
.\}
.PP
Create table
cinemas
in tablespace
diskvol1:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE TABLE cinemas (
        id serial,
        name text,
        location text
) TABLESPACE diskvol1;
.fi
.if n \{\
.RE
.\}
.PP
Create a composite type and a typed table:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE TYPE employee_type AS (name text, salary numeric);

CREATE TABLE employees OF employee_type (
    PRIMARY KEY (name),
    salary WITH OPTIONS DEFAULT 1000
);
.fi
.if n \{\
.RE
.\}
.SH "COMPATIBILITY"
.PP
The
CREATE TABLE
command conforms to the
SQL
standard, with exceptions listed below\&.
.SS "Temporary Tables"
.PP
Although the syntax of
CREATE TEMPORARY TABLE
resembles that of the SQL standard, the effect is not the same\&. In the standard, temporary tables are defined just once and automatically exist (starting with empty contents) in every session that needs them\&.
PostgreSQL
instead requires each session to issue its own
CREATE TEMPORARY TABLE
command for each temporary table to be used\&. This allows different sessions to use the same temporary table name for different purposes, whereas the standard\*(Aqs approach constrains all instances of a given temporary table name to have the same table structure\&.
.PP
The standard\*(Aqs definition of the behavior of temporary tables is widely ignored\&.
PostgreSQL\*(Aqs behavior on this point is similar to that of several other SQL databases\&.
.PP
The standard\*(Aqs distinction between global and local temporary tables is not in
PostgreSQL, since that distinction depends on the concept of modules, which
PostgreSQL
does not have\&. For compatibility\*(Aqs sake,
PostgreSQL
will accept the
GLOBAL
and
LOCAL
keywords in a temporary table declaration, but they have no effect\&.
.PP
The
ON COMMIT
clause for temporary tables also resembles the SQL standard, but has some differences\&. If the
ON COMMIT
clause is omitted, SQL specifies that the default behavior is
ON COMMIT DELETE ROWS\&. However, the default behavior in
PostgreSQL
is
ON COMMIT PRESERVE ROWS\&. The
ON COMMIT DROP
option does not exist in SQL\&.
.SS "Non\-deferred Uniqueness Constraints"
.PP
When a
UNIQUE
or
PRIMARY KEY
constraint is not deferrable,
PostgreSQL
checks for uniqueness immediately whenever a row is inserted or modified\&. The SQL standard says that uniqueness should be enforced only at the end of the statement; this makes a difference when, for example, a single command updates multiple key values\&. To obtain standard\-compliant behavior, declare the constraint as
DEFERRABLE
but not deferred (i\&.e\&.,
INITIALLY IMMEDIATE)\&. Be aware that this can be significantly slower than immediate uniqueness checking\&.
.SS "Column Check Constraints"
.PP
The SQL standard says that
CHECK
column constraints can only refer to the column they apply to; only
CHECK
table constraints can refer to multiple columns\&.
PostgreSQL
does not enforce this restriction; it treats column and table check constraints alike\&.
.SS "EXCLUDE Constraint"
.PP
The
EXCLUDE
constraint type is a
PostgreSQL
extension\&.
.SS "NULL \(lqConstraint\(rq"
.PP
The
NULL
\(lqconstraint\(rq
(actually a non\-constraint) is a
PostgreSQL
extension to the SQL standard that is included for compatibility with some other database systems (and for symmetry with the
NOT NULL
constraint)\&. Since it is the default for any column, its presence is simply noise\&.
.SS "Inheritance"
.PP
Multiple inheritance via the
INHERITS
clause is a
PostgreSQL
language extension\&. SQL:1999 and later define single inheritance using a different syntax and different semantics\&. SQL:1999\-style inheritance is not yet supported by
PostgreSQL\&.
.SS "Zero\-column Tables"
.PP

PostgreSQL
allows a table of no columns to be created (for example,
CREATE TABLE foo();)\&. This is an extension from the SQL standard, which does not allow zero\-column tables\&. Zero\-column tables are not in themselves very useful, but disallowing them creates odd special cases for
ALTER TABLE DROP COLUMN, so it seems cleaner to ignore this spec restriction\&.
.SS "WITH Clause"
.PP
The
WITH
clause is a
PostgreSQL
extension; neither storage parameters nor OIDs are in the standard\&.
.SS "Tablespaces"
.PP
The
PostgreSQL
concept of tablespaces is not part of the standard\&. Hence, the clauses
TABLESPACE
and
USING INDEX TABLESPACE
are extensions\&.
.SS "Typed Tables"
.PP
Typed tables implement a subset of the SQL standard\&. According to the standard, a typed table has columns corresponding to the underlying composite type as well as one other column that is the
\(lqself\-referencing column\(rq\&. PostgreSQL does not support these self\-referencing columns explicitly, but the same effect can be had using the OID feature\&.
.SH "SEE ALSO"
ALTER TABLE (\fBALTER_TABLE\fR(7)), DROP TABLE (\fBDROP_TABLE\fR(7)), CREATE TABLESPACE (\fBCREATE_TABLESPACE\fR(7)), CREATE TYPE (\fBCREATE_TYPE\fR(7))
